Chapter 7 Fire Protection

Transcription

1 Chapter 7 Fire Protection 7.1 Risk and Fire Protection Planning Fire Detection System Fire Alarm Center and Systems Engineering Alarm and Evacuation Fire Extinguishing Systems 145

2 7 Fire Protection For effective fire protection, two conditions have to be fulfilled: Firstly, the fire must be detected quickly and clearly and signaled. And secondly, correct measures must be implemented as quickly as possible. This is the only way to avoid direct fire and consequential damage or at least to keep this to a minimum. 7.1 Risk and Fire Protection Planning 7 The term 'risk' expresses the degree of danger. The risk factor is received by multiplying the probability of occurrence of an event with its impacts. The probability of occurrence has to be determined for each room individually. The term 'impacts' combines all expectable consequences of the event. Therefore, all consequences also those outside the room have to be detected and the individual results be added to calculate the impacts. The risk is then calculated by multiplying the impacts with the probability of occurrence. A possible procedure is shown in Table 71/1. The calculated risk levels (R = P I) are listed in Table 71/2. Fire protection planning is based on a risk analysis as described above. The task definition for this is to find out how the defined protection goal can be attained with an assignment of means as economical as possible. The result of this work is the fire protection concept. Among other things, the following factors have to be taken into account: Physical principles (fire development, smoke, flame propagation, etc.) Building conditions (basic structure, geometry, escape routes, ventilations, infrastructure such as energy channels, installations, etc.) Boundary conditions of the building operator (fixed and variable fire loads, processes, personnel organization, etc.) Probability of occurrence (P) Impacts (I) 1 = very likely 1 = few or none Hazardous to life 2 = unlikely 2 = medium and/or material assets (tangible 3 = likely 3 = high or intangible) 4 = occasionally 4 = very high 5 = frequently 5 = existence-threatening Risk = probability of occurrence impacts Table 71/1: Table for determining the risk level Risk level (R) Description Table 71/2: Risk levels and urgency Priority level Urgency of protective measures 18, 20, 25 Highest risk 1 Immediately 8, 9, 10, 12, 15 High risk 2 Short-term 4, 5, 6 Medium risk 3 Medium-term 2, 3 Low risk 4 Long-term 1 Negligible risk 5 Not required 140 Totally Integrated Power Fire Protection

3 Checklist Risk minimization in fire protection Flammable gases, liquids and materials have to be stored at safe places. Larger quantities of chemicals have to be stored in such a way that as few chemical reactions as possible take place. Acids and bases, for example, have to be stored separately. Areas with dangerous goods have to be provided with corresponding information and no-smoking signs. Fire loads not required, e.g. flammable materials which are not immediately required, are not to be stored at the workplace but at a safe place. The waste management is to be designed such that no flammable waste at all gathers outside the areas intended for it. Heaters, fan heaters, etc. are a particular fire risk. It has to be ensured that the safe distances to flammable materials are kept. Therefore, portable or not permanently mounted fan heaters should be abandoned, if possible. Specifically identified smoking areas with ashtrays etc. allow for a disciplined handling of tobaccos. This prevents an uncontrolled disposal of cigarette stubs and matches. Up to 40% of the fires are caused by arson. With an access control system, the access to critical areas can be controlled and thus the risk of arson, in particular by strangers, be reduced. Most of the cases of electric firing occur while the device is in standby mode. Therefore, instruments which are not required should be switched off with the power switch whenever possible. Cable extensions and power strips have to be avoided wherever possible. Electrical appliances and the electric wiring have to be checked periodically by a specialist. Fuses have to comply with the device requirements and installations. The smoke and flame propagation between rooms and fire areas have to be prevented with suitable measures. Fire doors either have to be kept closed or it must be possible to close them automatically in case of a fire via automatic closing mechanisms. The functional reliability of the closing mechanisms is to be ensured with periodical, preventive maintenance. In the area of fire doors, no objects at all must be deposited. Moreover, fire doors have to be signed accordingly. Emergency exits preferably have to lead directly to safe streets/places. Emergency exits to enclosed inner courtyards are not permissible, for example, since it would not be possible to increase the distance to the building, if necessary. Emergency exits have to be well signed and lit also in case of an emergency. It has to be ensured that emergency exits are not blocked with furniture, wheelbarrows, etc. Emergency exits have to be safely walkable. This includes the state of the floors (no loose carpets, smooth surfaces, etc.) as well as the danger of falling due to obstacles (electric cables or wet floors). Doors in emergency exits have to open up to the outside and it must always be possible to open them from the inside. In case of misuse, a key box with a glass to be broken or a door alarm (alarm goes off as soon as the door is opened) might help. However, this requires clear, easily understandable information signs. It has been proved that the quickest possible fire alarm is effected by an automatic fire detection system. Its operability is to be ensured via periodical, preventive maintenance. A fire detection system has to alarm the fire department either directly or via an alarm receiving station. The personnel is to be trained such that a quick, correct alerting and an ordered evacuation of the building is ensured. Hand fire extinguishers and fire blankets allow for a quick extinguishing of emerging fires and therefore have to be positioned at well visible places in sufficient quantities. The personnel has to be imparted the basics of firefighting and trained the use of fire-fighting equipment for manual fire-fighting (hand fire extinguisher, fire blanket, etc.). If the use of the building has been changed, the fire precautions have to be reviewed and adapted, if necessary. The risk analysis and fire protection planning have to be kept and continuously adapted to the changes. Fire insurance companies often give valuable hints how to improve the fire protection for real property. 7 Totally Integrated Power Fire Protection 141

4 7 7.2 Fire Detection System A fire detection system consists of the individual detectors and the fire alarm center. The components are to ensure quick and spurious-safe alerting. To this end, the individual components have to be optimally matched. Intelligent, high-speed evaluation models of advanced fire detection systems such as the SINTESO detectors with ASA (Advanced Signal Analysis) technology enable smoke and fire to be detected immediately and spurious-safely, no matter how difficult the environmental conditions. These detectors can be programmed optimally for the conditions at the location of use. Point-type smoke detectors Point-type smoke detectors are installed at the ceiling or at the place at which the propagation and accumulation of the fire parameter smoke is to be expected. Point-type multi-sensor smoke detectors which detect smoke and heat simultaneously are to be placed like point-type smoke detectors. Point-type smoke detectors may normally be used up to a room height of 12 m. With the room height increasing, the smoke density at the ceiling decreases because the given quantity of smoke is distributed in a larger air volume. Moreover, the cooling smoke is no longer able to permeate the heat cushion at the ceiling of high rooms. The following conclusions can be drawn from that: With the room height increasing, the response sensitivity of the fire alarm system has to be higher or an increasingly larger initial fire is required for alarm release. the monitored area per smoke detector may be increased. the smoke of smoldering fires decreasingly reaches the ceiling and thus the detectors. the smoke detectors have to be detached ever further from the ceiling. Point-type heat detectors In contrast to smoke detectors, heat detectors are to be installed at the highest point of the ceiling. In order to prevent false alarms and nevertheless ensure a justifiable response behavior, the static response temperature of heat detectors has to range between 10 C and 35 C above the highest temperature which may occur due to natural or operational influences in the area surrounding the detector. Class A1 heat detectors may normally be used up to a room height of 7.5 m. The temperature increase at the ceiling directly over the fire location decreases approximately quadratically with the room height increasing. This means that with the room height increasing, the response sensitivity of the heat detectors has to be higher or an increasingly larger fire is required for alarm release. The monitored area depends on the size of the room to be monitored and the slope of the ceiling. In the case of sloping ceilings, the heat along the ceiling slope increases up to the highest point. This results in a heat concentration in the roof ridge. This is why in the case of sloping roofs, the basic monitored area and the detector distance may be increased. Linear smoke detectors A linear smoke detector consists of a transmitter and a receiver for infrared light and works similar to a light barrier. It is installed below the ceiling on the wall. There must be a permanent, interference-free line of sight between the detector and reflector. The monitoring beam must not be interrupted by moving objects such as overhead traveling cranes, ladders, suspended advertising media or other movable objects. The detector has to be installed permanently and unmovable. Here, it also has to be kept in mind that flexible wall constructions are unsuitable because a too large deflection of the monitoring beam prevents reliable detection. Concrete and brick walls fulfill these requirements. Wood and steel constructions are mostly unsuitable because changes of temperature and humidity, wind or snow pressure can influence such constructions. Heat cushions below the ceiling can prevent the rising smoke from reaching the ceiling. The linear smoke detector therefore has to be installed below a heat cushion to be expected. In the case of room heights above 12 m, the distance to the ceiling should range between 60 and 120 cm. To ensure that smoldering fires or smaller fires with low fire thermal can also be detected in high rooms, a second or possibly a third detector has to be installed at the assumed height of the smoke propagation of the smoldering fire. This level differentiation becomes important in the case of rooms with a height of 6 m or higher. Detectors of the lower monitoring level should be arranged in an offset pattern compared to the top monitoring level. 142 Totally Integrated Power Fire Protection

5 7.3 Fire Alarm Center and Systems Engineering The fire alarm center evaluates the signals from the peripheral devices, controls the alarm and fire control system and is furthermore the point of interaction between persons and the system. The term 'systems engineering' compasses all components of a fire alarm system including their communication, i.e. the networking of the field elements (sensors and actuators) with the fire alarm center and possibly several fire alarm centers among each other as well as with higher-level management systems (Fig. 73/1). A modern fire alarm center provides the following functional features: Simple and safe system operation Flexible system design with regard to size and structure Free adaptation of the central organization to changing customer requirements The battery capacity has to be dimensioned such that the unrestricted operation of the fire alarm system is possible during the requested emergency operation time and that the alarm devices can be supplied for at least another 30 minutes after the end of the emergency operation time. The use of monitored remote power supply units is permitted. Signals from the remote power supply units are to be displayed in the control center like fault indications. With regard to the assumption of interference signals and troubleshooting, emergency power transitory periods in accordance with Table 73/1 are recommended. Freely programmable control outputs for the use of fire control systems Event memory which stores hundreds of events, sorted according to information classes, and provides them when required Integrated emergency operation functions so that in the event of the failure of a signal processing unit, a reliable fire alarm can still be guaranteed Real-time clock with date and automatic change-over to summer and winter time The functional scope of each system for a specific case has to be clarified in advance. Lines interface Fire alarm center (CPU) Control interface 7 Power supply Commissioning Maintenance The power supply provides the required energy for the fire alarm system. In accordance with EN 54, two independent power sources have to guarantee the power supply for the fire alarm center in parallel stand-by mode. Both power sources have to be dimensioned such that in the event of the failure of one source, the operation of the system and the alarm installations can be maintained for a certain period of time. The following has to be taken into account for that: One of the two power sources has to be a permanent mains supply, the other one a battery or similar source. Parallel operation is required in which the correspondingly dimensioned charger supplies the fire alarm system and simultaneously charges the batteries connected in parallel. The emergency power supply of the fire alarm system has to be effected via a separately secured feeder line. Fig. 73/1: Fire alarm center and systems engineering Emergency power criteria Without interference signal transmission to a permanently manned control center (for bridging weekends) With interference signal transmission to an internal or external, permanently manned control center With interference signal transmission to a permanently manned control center, secured mains connection (e.g. emergency-power diesel generator for 24/7 operation) Emergency operation time [h] Table 73/1: Emergency operation time demanded by EN Devices which are not part of the fire alarm system must not be connected to the power supply of the system. Totally Integrated Power Fire Protection 143

6 7 7.4 Alarm and Evacuation Man's five senses are all suitable for alerting, but most of all hearing and eye-sight. Of that, sound is preferred for alerting because it penetrates walls and can easier wake up persons. Therefore, planning most of all focuses on sound alarm and voice alarm. For a successful self-rescue, voice alarm has by far the best attributes: Persons respond virtually instantly. Giving reasons for the alarm will convince the building users of the necessity of the requested reaction. The big advantage of the voice alarm systems is that the affected persons are immediately communicated the correct reaction. Voice alarm systems A voice alarm system is an alarm system which uses electronically stored voice announcements as well as acoustic signals for alerting in case of an emergency. The voice alarm system can be activated either manually or automatically, e.g. via an alarm of the fire alarm system, and the pre-programmed evacuation process be initiated. The system typically transmits an alarm signal, e.g. a gong or whistling sound, followed by a recorded voice announcement. The system is usually operated in the automatic mode in the first minutes after the alarm. In a later phase, e.g. after the arrival of the fire brigade, individual instructions can be communicated by the firefighters or other authorized personnel. To this end, instructions adapted to the current situation of danger are spoken into a microphone. The system transmits these instructions directly to the selected loudspeaker zones in the building (live announcement). Voice alarm systems are often also used as a normal electro-acoustic loudspeaker system (ELS) for other communication purposes, e.g. for calling persons, advertising and the transmission of background music. The building operator thus has an additional high-quality transmission system with a high failure safety at his disposal. Provided that, however, the voice alarm provides for a fully automatic priority control to ensure that in case of an alarm, the information of the voice alarm system is automatically prioritized. Building evacuation procedure Modern voice alarm systems master the fully automatic, successive building evacuation, i.e. the building is evacuated automatically and successively. This has the following advantages: Reduced capacity peaks on the escape routes and in the staircases: If the whole building is evacuated at once, the persons on all floors pour into the staircases at the same time, which might lead to tailbacks. Lower probability of panic: The awareness of being exposed to a danger and not being able to do anything (blocked exits) can easily induce a panic. A panic can definitely have worse consequences than the actual fire. Limitation of the evacuation to the necessary extent: The evacuation of an entire building is only necessary if the fire cannot be brought under control any more. In most cases it is sufficient to evacuate one or several fire area(s). The procedure of also evacuating the floor located below the point of origin of the fire in the first phase gains acceptance. Depending on the region and conventions, the top floor and the entire basement can be evacuated additionally and simultaneously. If the fire spreads out, the remaining floors which were asked to wait in a warning notice during the first evacuation phases are evacuated one after the other in the following evacuation phases (Fig. 74/1). Evacuation in... Phase 3 Phase 2 Phase 2 Phase 3 Phase 2 Phase 3 Burst of fire Fig. 74/1: Example of a successive evacuation of buildings 144 Totally Integrated Power Fire Protection

7 7.5 Fire Extinguishing Systems Combustion is nothing but a chemical oxidation process of a combustible and the ambient air. The oxidation process can be subdivided into three different subprocesses. According to the manner in which the oxidation takes place, the following different processes can be differentiated: Smoldering fire, the decomposition of materials under heat Glowing fire, in which the combustible burns softly without a flame Flame fire or open fire Depending on the state of aggregation of the burning material, different types of fire result. The diagram in Fig. 75/1 shows the interrelations. Automatic fire extinguishing systems are supposed to either extinguish or suppress emerging fires to protect objects, rooms or whole buildings from fires and their consequences. The extinguishing agents used in that are either liquid (water), biphasic (foam), solid (powder) or gaseous (gases). Depending on the extinguishing agent, they either extract heat from the fire and/or repress the oxygen or separate it from the combustible. The effect of extinction or suppression starts with the flooding time and ends after the expiration of the hold time. Interventions and automatic extinguishing systems have to be coordinated correspondingly. Flooding time is the time elapsing from the triggering of the extinction until the required extinction concentration is achieved. Hold time is the time during which the extinguishing system maintains the required concentration by continuously supplying the extinguishing agent. Gaseous extinguishing systems use either natural gases or chemical quenching gases. While natural gases mainly repress the oxygen, chemical quenching gases engage with the combustion process. Most well-known are halons which have been prohibited in the meantime for reasons of environmental protection, while the environmental compatibility of today's extinguishing gases is undoubted. Gaseous extinguishing agents are stored in pressure tanks. The system layout as well as the correct output of the extinguishing agent with sufficient pressure are decisive for the correct functioning of the fire extinguishing system, which is not yet self-evident. The selection of the best suitable fire extinguishing procedure, the correct system layout and the correct integration of the fire extinguishing system in the building management requires experience and extensive knowledge. gaseous liquid solid Fig. 75/1: Type of fire with regard to the state of aggregation 7 Water is the most common extinguishing agent and is used in various sprinkler systems as well as in spray deluge and water mist extinguishing systems. While sprinkler systems are usually triggered temperature-dependent by the sprinkler heads, other extinguishing procedures are usually activated separately by automatic fire detectors. A wide variety of foam extinguishers with most different fields of application is obtained with the help of various foaming agents and the varying admixing of compressed air. Powder extinguishing systems are by contrast less common since they are advantageous only under certain conditions. Totally Integrated Power Fire Protection 145

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